1. Field of the Invention
This invention relates generally to incandescent illumination systems, and particularly to a filament array for an incandescent lamp for use in combination with a concave reflector.
Incandescent lamps of this kind are typically used in theater, film, television, architectural and other general purpose lighting fixtures that provide high-intensity beams of light. It is desirable in such fixtures to collect as much of the light emitted by the lamp as possible, and project that light forward in a high-intensity beam.
2. Discussion of the Art
One commercial embodiment of a system of this type, known commercially as the xe2x80x9cSource Fourxe2x80x9d system, is described in U.S. Pat. No. 5,268,613. In this system, a high intensity beam is generated using a filament with a multiplicity of helically-wound coils arranged in a substantially symmetrical pattern around the longitudinal axis of the lamp. There are two main commercial embodiments of this invention, which necessarily differ because of the demands of the voltage supply to the lamp. Lamps designed for operation on 115 V or 120 V supplies typically have four coils which, when viewed in plan, are arranged in a substantially square pattern around the longitudinal axis of the lamp, whereas lamps designed for operation at voltages between 220 V and 240 V typically have six coils which, when viewed in plan, are arranged in a substantially hexagonal pattern around the longitudinal axis of the lamp.
It is well understood amongst those skilled in the art, and has become even more apparent since the Source Four system was first commercialized, that the proportion of light collected by the reflector and projected forward into the beam could be substantially increased if the overall space occupied by the filament structure could be minimized. This has been achieved in the case of lamps designed for operation at 115 V and 120 V through the implementation of better control procedures in manufacturing and the use of arc-preventing gas fills in the lamp capsule. However, it has been found that the six-filament structures used at higher voltages, typically 220 V-240 V, become less reliable when made more compact in their existing form because the resulting high voltage gradient between the current-carrying wires leads to a high risk of arcing. Attempts have been made to overcome this by re-arranging the order in which the filament sections are joined together in series. However, this has necessitated the use of complex support structures which are difficult (and often costly) to manufacture on a consistent basis. Furthermore, such structures involve the precise placement of filament support hooks in 3-dimensional space in order to achieve the desired filament geometry. Any deviation from this precise placement requirement can have two detrimental effects. Firstly, the quality of the output of the lamp in its fixture is adversely affected, and secondly, there is an opportunity for sections of the filament and its support structure to be accidentally positioned too close to other sections of the same structure. In these cases, the lamp becomes susceptible to arc-out when it is subjected to vibrations in service. Hence the incidences of premature failure may be significantly increased.
It would be desirable, therefore, to link the filament sections together in such a way as to eliminate arcing, while at the same time simplifying the support structure for the filament support hooks.
According to the present invention, there is provided a filament array for an incandescent lamp comprising at least five filament sections having their longitudinal axes parallel with one another and, when viewed in plan, being arranged substantially symmetrically in a polygonal configuration around the lamp axis; the filament sections being wound from a single wire and being electrically connected together in series by means of linking sections of said wire extending between corresponding ends of the filament sections, with alternate linking sections being positioned at opposite ends of the filament sections; the linking sections at the two ends of the array being supported by a set of support members extending from respective frame members; and with the electrical input and output of the array being through terminal wire sections on opposite or substantially opposite sides of the array; characterized in that the linking sections are configured such that said set of support members at each end of the array are substantially collinear, and said frame members each comprise a single straight member.
The present invention is suitably incorporated in an incandescent lamp adapted for use with a concave reflector to produce a high-intensity beam of light. The incandescent lamp comprises a plurality of linear, helically-wound filament sections which, when viewed in plan, are arranged with their longitudinal axes substantially parallel with each other, and arranged in a substantially symmetrical pattern in a polygonal configuration around the longitudinal axis of the lamp. The filament sections are electrically linked together in series. Each section is linked to an adjacent section by means of a linking section, referred to in the art as a loop. The filament structure may comprise loops of three or more different lengths.
The filament structure of the invention comprises a more compact filament than is currently available, and can be mounted onto its support frame in a simplified way without the need for the complex positioning of the hooks in 3-dimensional space, thus eliminating the risk of hot shock and early life arcing.